1. Technical Field
The present invention relates to an actuator device including piezoelectric elements displaceably provided on a substrate, and to a liquid-jet head using the actuator device.
2. Related Art
An actuator device including piezoelectric elements, each of which is displaced by application of a voltage, is used as, for example, a liquid-ejecting unit for a liquid-jet head mounted on a liquid-jet apparatus, which jets a liquid droplet. As such a liquid-jet head, for example, the following type of ink-jet recording head has been known. In the type of ink-jet recording head, a part of a pressure-generating chamber communicating with a nozzle orifice is formed of a vibration plate, which is deformed with the piezoelectric element. With the deformation, ink in the pressure-generating chamber is pressurized, and thus ink droplets are ejected from the nozzle orifice.
As an ink-jet recording head of this type, the following one has been proposed. Specifically, in the ink-jet recording head, a lower electrode is provided along a direction of the shorter sides of a plurality of piezoelectric elements. Then, lower electrode removed portions are provided by removing a region in the lower electrode between each adjacent two of the piezoelectric elements so as to have a thickness smaller than that of a region where each piezoelectric element is formed (for example, refer to p. 14 and FIG. 16 of JP-A-2005-94688).
In another ink-jet recording head that has also been proposed has a lower electrode removed portion provided on each side of the piezoelectric elements in the width direction of each piezoelectric element. In each lower electrode removed portion, a part of a lower electrode is partially removed so as to be formed into a thin film (for example, refer to p. 16 and FIG. 6 of JP-A-11-151815).
The configuration with lower electrode removed portions, such as ones disclosed in JP-A-2005-94688 and JP-A-11-151815, has the following advantage that the displacement characteristics of the vibration plate are improved, which results in an improvement in the displacement characteristics of each piezoelectric element. As a result, the ink-ejecting characteristics are improved. The above configuration, however, has a problem. Specifically, in the above configurations, stresses are concentrated on portions, such as a corner defined by the lower electrode removed portions. As a result, the drive durability is deteriorated.
Moreover, in a case where a protective film having moisture resistance is provided to the piezoelectric elements, another problem occurs. Specifically, when the protective film is formed, a surface unevenness or the like occurs in the protective film due to a corner defined by the lower electrode removed portion. As a result, the part of the protective film where the surface unevenness occurs is cracked by the drive of the piezoelectric elements.